Prosthodontics & Occlusion · patient case question
With only 0.5 mm of remaining sound tooth structure above the margin, what is the principal concern?
Patient case: Restoring a broken-down tooth
demo: 45-year-old female
chief: Wants to restore a heavily broken lower molar and to improve the appearance of her upper front teeth.
history: Nothing relevant medically. She has had a crown placed on tooth 12 elsewhere.
meds: None.
findings: Tooth 30 has minimal remaining coronal structure with 0.5 mm of sound dentin above the crown margin circumferentially. An impression and a working cast from the first attempt show voids at the margin and a torn finish line. The crown on tooth 12 is markedly brighter than the adjacent very yellow natural teeth.
Show answer and explanation
Correct answer: B. Inadequate ferrule height
- A. Shade is an esthetic consideration and is not the structural concern that governs whether this tooth is restorable.
- B. Correct. A ferrule requires at least 1.5 to 2 mm of sound circumferential dentin coronal to the finish line, encircled by the crown. That band resists the wedging force of a post and protects against vertical root fracture. At 0.5 mm there is effectively no ferrule, and crown lengthening or orthodontic extrusion is needed before restoring.
- C. The problem is too little remaining tooth structure, not too much reduction.
- D. Pulpal protection is not the issue in a tooth this broken down, which will be endodontically treated in any case.
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